1. Field of the Invention
The present invention relates to a contactless communication medium that performs contactless wireless communication with a reader/writer in proximity, an antenna pattern arrangement medium provided in the contactless communication medium, a communication apparatus incorporating the contactless communication medium, and a communication method for contactless wireless communication.
2. Description of the Related Art
So-called contactless IC cards are commonly used as a contactless communication medium that performs contactless wireless communication with a reader/writer in proximity. The contactless IC cards are widely used, for example, for ticket examination systems in railway stations, payment systems in convenience stores and so forth, room entry/exit systems, and so forth. The contactless IC cards are also referred to as RFID (Radio Frequency Identification) tags or wireless IC tags.
Such a contactless IC card includes an IC chip embedded inside the card, which allows quick reaction and processing for room entry/exit and billing management, and thus enhances the convenience of the card compared to a magnetic card.
FIGS. 11A and 11B show an exemplary configuration of a contactless IC card according to the related art. FIG. 11A shows a circuit for contactless communication disposed on a resin base material. In a contactless IC card as an actual product, the circuit is concealed by an outer shell material such as a film disposed on the front surface of the card.
The configuration shown in FIG. 11A is described. An antenna coil portion 20 is disposed on the front surface of a base material 10 close to the outer periphery of the base material 10. The antenna coil portion 20 is formed by winding a conductor pattern made of a conductor such as copper or aluminum and having a constant width in a plurality of turns (in the example, four turns) at constant intervals on the surface of the base material 10 close to the outer periphery of the base material 10.
A first end portion 21 and a second end portion 22 of the antenna coil portion 20 are connected to an IC chip 11 serving as an integrated circuit component that performs a communication process. In this case, the first end portion 21 of the antenna coil portion 20 is led to the back surface of the base material 10 to be connected to the IC chip 11, which performs a communication process, via a conductor pattern 14 provided on the back surface. The second end portion 22 of the antenna coil portion 20 is connected to the IC chip 11 via a conductor pattern 13.
The first end portion 21 and the second end portion of the antenna coil portion 20 are also connected to a capacitor 12 and an adjustment capacitor 30. The first end portion 21 of the antenna coil portion 20 is connected to the capacitor 12 and the adjustment capacitor 30 also via the conductor pattern 14 provided on the back surface.
The capacitor 12 accumulates charge generated by a carrier wave received by the antenna coil portion 20 to obtain electric power for driving the IC chip 11, and includes a first electrode portion formed by a conductor pattern provided on the front surface and a second electrode portion formed by a conductor pattern provided on the back surface. The capacitor 12 accumulates charge with the first electrode portion and the second electrode portion, which face each other via the base material 10. Each of the electrode portions forming the capacitor 12 has a relatively large area so as to be able to accumulate a relatively large amount of charge.
The adjustment capacitor 30 is configured to change the resonant frequency. The adjustment capacitor 30 includes a first conductor pattern 31 provided on the front surface and connected to the second end portion 22 of the antenna coil portion 20 and a second conductor pattern 32 provided on the back surface and connected to the conductor pattern 14. The first conductor pattern 31 provided on the front surface is formed to include comb-teeth conductor patterns. The second conductor pattern 32 provided on the back surface is formed to orthogonally intersect the comb-teeth portions. Charge is accumulated at each of the intersections. The adjustment capacitor 30 has a small capacitance compared to the capacitor 12. The adjustment capacitor 30 increases the resonant frequency by cutting off some of the comb-teeth conductor patterns to reduce the condenser capacitance during adjustment of the resonant frequency in a contactless IC card manufacturing process.
FIG. 11B shows a circuit that is equivalent to the configuration of the contactless IC card shown in FIG. 11A.
As shown in FIG. 11B, the IC chip 11 and the capacitor 12 and the adjustment capacitor 30 are connected in parallel with the antenna coil portion 20.
The adjustment process for increasing the resonant frequency using the adjustment capacitor 30 is performed by cutting off portions of the first conductor pattern 31 and the second conductor pattern 32. In the process, for example, a hole is formed in the base material 10 at a point at which the first conductor pattern 31 is cut, and the first conductor pattern 31 and the second conductor pattern 32 are removed.
The resonant frequency adjustment process in the manufacturing process is performed automatically using an adjustment device (not shown). That is, the adjustment device is provided with data on a cutting position for correcting the resonant frequency of a communication medium in advance, and performs adjustment by determining a cutting position on the basis of a resonant frequency obtained through actually measurement and forming a hole in a base material at the determined position. By performing the adjustment, a contactless IC card with an appropriate resonant frequency is obtained.
FIGS. 12A and 12B show an exemplary configuration of a contactless IC card, which is different from the example of FIGS. 11A and 11B, with an intermediate tap.
The configuration shown in FIG. 12A is described. An antenna coil portion 20, which is formed by winding a conductor pattern in a plurality of turns, is disposed on the front surface of a base material 10 close to the outer periphery of the base material 10. A first end portion 21 and a second end portion 22 of the antenna coil portion 20 are connected to an IC chip 11 serving as an integrated circuit component that performs a communication process. The first end portion 21 of the antenna coil portion 20 is connected to the IC chip 11, which performs a communication process, via a conductor pattern 14 provided on the back surface.
The capacitor 12 is connected to the first end portion 21 of the antenna coil portion 20 on the back surface, and to an end portion 24 of an antenna extension portion 23 extending from the second end portion 22 of the antenna coil portion 20 on the front surface.
Regarding the adjustment capacitor 30, the second conductor pattern 32 provided on the back surface is connected to the conductor pattern 14 provided on the back surface, and the first conductor pattern 31 provided on the front surface is connected to the end portion 24 provided on the front surface.
FIG. 12B shows a circuit that is equivalent to the configuration of the contactless IC card shown in FIG. 12A.
As shown in FIG. 12B, the IC chip 11 is connected to the antenna coil portion 20, and the capacitor 12 and the adjustment capacitor 30 are connected to the antenna coil portion 20 via the antenna coil portion 20 and the extension portion 23. The second end portion 22, at which the antenna coil portion 20 and the extension portion 23 are connected to each other, serves as an intermediate tap. The adjustment process performed using the adjustment capacitor 30 is the same as the example of FIGS. 11A and 11B.
In the case of the configuration shown in FIGS. 12A and 12B, adjustment performed using the adjustment capacitor 30 makes it possible to change the overall inductance value without changing the inductance value of components connected to the IC chip 11.
Japanese Unexamined Patent Application Publication No. 2007-102348 discloses an RFID tag in which a dummy pattern is provided outside an antenna coil.